Cathode ray television system



Allg- 1936- D. PRINZ 2,050,528

CATHODE RAY TELEVISION SYSTEM Filed Feb. 29, 1932 '0 recewer anddezeviar INVENTOR DIETRKZH lNZ :ATTORNEY Patented Aug. 11, 1936 UNITEDSTATES PATENT OFFEQE Dietrich Prinz, Berlin,

Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphicin. b. H., Berlin, Germany, a corporation of Germany ApplicationFebruary 29, 1932, Serial No. 595,817 In Germany March 2, 1931 12Claims.

The present invention relates to an improvement in television systemsand covers an improvement in the general type of system disclosed by mypatent application Serial No. 581,217, filed December 15, 1931, nowPatent No. 2,011,260,

granted Aug. 13, 1935.

The aforementioned patent application relates to a circuit schemeadapted to insure variations of brightness of the luminous spotsproduced on the fluorescent end viewing wall of a Braun tube, and isparticularly adapted for use in television work.

As shown by my above identified patent, a cathode ray tube is used asthe medium by which electro-optical images may be reconstructed atvarious viewing points. In such type of tubes it is customary to providea cathode as the electron emitting element and the electron streamemitted is arranged to pass through a tubular shaped anode element, andthen between the two auxiliary deflector plates used as intensitycontrolling elements, after which the ray passes through a suitablediaphragm. The diaphragm controls the electron stream passing toward thefluorescent end wall of the tube. The electron stream which passesthrough the diaphragm is then caused to pass through the space betweentwo deflector plate pairs which are positioned at right angles to eachother to control the path of projection of the cathode ray in a mannerknown in the art. It is customary to connect one plate of each of thesaid pairs of deflecting plates with the grounded anode. It is only whenthe potentials prevailing at the auxiliary'intensity control plate is ofzero value or nearly zero value that the cathode ray pencil will be ableto pass through the screening diaphragm.

As, has been shown by my above identified patent, an undulatingunidirectional potential is applied to the auxiliary intensity controlplate so that the cathode ray pencil will find a chance to pass throughthe diaphragm only during the extremely brief periods of time when thepulsating D. C. waves supplied as controlling impulses pass throughzero. Thus, by altering the pulsating D. C. potential it is possible tovary also the times during which the electron stream can pass beyond thediaphragm to reach the luminous or fluorescent screen with a resultantalteration also of the brightness of the impinging light spot producedby the applied pulsating D. C. potentials.

A scheme of this general arrangement involves the drawback that thebrightness of the light spot is inversely proportional to the suppliedpotential on the control plate, and for the purposes of television worka special modulation of the transmitter is required.

The object of the present invention is, therefore, to provide a linearor approximately linear relationship between the brightness of the spot5 and a potential fed to the tube. With this end in view the controlplate of the tube is supplied with apulsating D. C. potential the valueof which is zero not only for a brief instant, but rather for anappreciably long fraction of the period thereof.

Other objects and advantages of the invention will, of course, becomeapparent and at once suggest themselves to those skilled in the art towhich the invention relates by reading the following specification andclaims in connection with the accompanying drawing, wherein Figure lillustrates a cathode ray tube used for the production of anelectro-optical image in accordance with the present invention; Figure 2illustrates diagrammatically the form of the pulsating D. C. wavesupplied; by this figure portion A indicates a pulsating D. C. waveproduced by rectifying asymmetrically a sinusoidal wave, and portion 1)shows diagrammatically a pulsating D. C. produced by asymmetricallyrectifying a triangular wave shape. Fig. 3 shows diagrammatically theunderlying principles of the means used for producing the pulsating D.C. wave. Fig. 4 represents an embodiment of the scheme used to producethe pulsating D. C.

To refer to the drawing, the cathode ray tube I is provided with anelectron emitting cathode, generally designated as 2, which emits astream of electrons which are projected through a tubular anode 3 andthen through a set of deflecting plates 4 and 4, after which they arecaused topass through a diaphragm or screening member 5 provided with acentral aperture 6 of predetermined size. In order to control theposition at which the projected electron stream, conventionally shown bythe dotted line within the tube, strikes the fluorescent end wall I ofthe tube, deflecting plates 8, 8 and 9, 9 have been provided. Thesepairs of plates 8, 8' and 9,

9' are positioned at right angles to each other in a manner well knownin the art. It is of course, understood that the two sets of deflectingplates are supplied with suitable voltages for producing the scanningaction as is well known in the art. It is, of course, to be understoodthat electromagnetic fields might be substituted for the electrostaticfields produced by the deflecting plates in order to control theposition of the electron stream or beam in a manner well known in theart without departing from the 5 spirit and scope of this invention. Aswas taught in my above identified patent referred to, the controllingpotentials for controlling that portion of the cathode ray stream whichstrikes the fluorescent end wall I are supplied across the deflectingplates 4 and 4. The deflecting plates 4 and 4' are fed pulsating D. C.which is dependent upon the amplitude of the rectified output of theradia receiver 25 which receives radiant energy by means of the antenna24. Converting means 26 which supply the pulsating D. C. to the plates 4and 4' are discussed below in further detail in connection with Figs. 3and 4.

Fig. 3 shows schematically the principle of producing the pulsating D.C. in accordance with the rectified voltage received from the radioreceiver. In this figure, I0 represents a local oscillator producingalternating currents. 'II is a rectifier, I2 is a variable voltage whichrepresents the rectified output of the radio receiver 25, and I3 showsthe load resistor across which potentials are taken off to feed theplates 4 and 4. It will be observed in connection with Fig. 3 that ifthe voltage shown as a variable battery I2 is made zero, for example,true half-wave rectification takes place so that there will appearacross the resistance I3 a voltage whose wave shape will consist of thepositive half-cycles of a sinusoidal wave. If, however, the batteryvoltage is made equal to the peaked voltage of the alternating currentsupplied by the generator I0, then the wave shape across the resistor I3 will be pulsating D. C. whose wave shape will be a true sinusoidalwave and whose negative peaks will now coincide with the zero axis. Ifthe variable voltage I2 is now made negative and equal to the peakedvoltage, then the resultant output across the resistor I3 will be zerosince the superimposed D. C. leaves no voltage available for forcingcurrent through the rectifier I I. It will thus be apparent thatdependent upon the amplitude of the D. C., the spacing period,

as well as the amplitude, of the resulting voltage appearing across theresistor I3, will be determined. Thus we have, in efiect, a system whichwill produce interruptions of the cathode ray beam which are of constantfrequency but of variable duration. This feature provides an improvementover my invention described in Patent No. 2,011,260, issued August 13,1935, inasmuch as the individual marking period is not broken up into anumber of discrete marking and individual periods occuring at the rateof the modulated radio frequency wave.

The variable D. C. potential has the purpose of varying the length ofthe periods during which the pulsating D. C. potential is of zero value.If the said pulsating D. C. potential, for instance, is equal to zerothen the valve II will be permeable just during a half-period. If thepotential is equal to the crest value of the A. C. potential supplied bythe generator II], the valve, according to the polarity of the said D.C. becomes permeable either for the full period or else impermeable forthe full period, while intermediately all values are between zero andthe full period.

a It will be readily understood that even in the presenceof a pulsatingD. C. potential, such as is illustrated by Figure 2a, of the generatorII] the dependence of the blocking time upon the auxiliary potentialbecomes almost linear. A

strictly linear function is insured if the potential of the generator isnot sinuous, but of triangular wave shape as is illustrated y F g e 20.The production of A. C. potential of any desired frequency having atriangular curve shape is fundamentally known in the prior art (see, forinstance, Archiv fuer Elektrotechnik, vol. 21, Heft 5, page 471, 1929)If an arrangement as described is to be used for picture telegraphy workor for television then the variable potential I2 is derived from thelong-distance line or the rectifier of the television receiverapparatus.

Referring now to Fig. 4, it will be readily appreciated that the bridgecircuit shown is an actual embodiment of the schematic sketch of Fig. 3in which the battery I5 represents the rectified output of the detectedradio signal. The circuit arrangement shown in Fig. 4 is the converter26 of Fig. l, and it will be appreciated that the lead 22 is connectedto the plate 4 to produce the deflecting voltage for producing thepicture on the screen I. The generator I4 is the local source ofalternating current and maybe either sinusoidal or triangular, asexplained above, and the resultant output between the grounded point ofthe bridge and the lead 22 will then have a wave shape shown in Fig. 2aor 2b, depending on whether the oscillator I4 produces a sinusoidal waveor a triangular wave.

Where high frequencies are being dealt with, it may become necessary tocompensate the capacity of the valve II by means of a convenient circuitarrangement in order that the capacitive wattless current may notoccasion an undesired potential during the blocking period. A scheme ofthis sort is shown in Figure 4 wherein numeral I4 denotes the A. C.generator, I5 the, variable auxiliary potential or the potential derivedfrom the receiver, I6 the rectifier, such as a thermionic valve, and I!designates a condenser whose capacity is equal to the valve capacity; I8and I9 are two equal, resistances, and 2B is a resistance which at oneend is grounded by way of the potential source I5, while at the otherend 22 there is produced a potential which is to be fed to the auxiliarydeflector plate 4 of the tube shown by Figure 1. This arrangementconstitutes for the capacitive wattless currents a Wheatstone bridge sothat these currents will not contribute to the potential prevailing atpoint 22.

In lieu of a condenser I I it would also be feasible to use anothervalve having similar dimensions and characteristics to the valve I6. Thescheme then represents a. rectifier arrangement in which both halves ofthe wave are used.

While the invention has been illustrated in only its preferred forms, itis, of course, to be understood that many changes and modifications willbecome apparent and suggest themselves to those skilled in the art towhich the invention relates and I therefore believe myself to beentitled to make and use all modifications of the invention which fallfairly within the spirit and scope of the invention as defined by thehereinafter appended claims.

Having now disclosed my invention, what I claim and desire to secure byLetters Patent is the following:

1. The combination of a cathode ray device having deflecting electrodesand means for applying rectified deflecting potentials theretocomprising electrical network comprising the series combination of analternating current source, a halfwave rectifier and a resistanceelement, and means for applying to the network a variable direct currentvoltage to control the zero period leg thereofand a capacity element forcompensating forthe watt-less current flowing forming the fourth legthereof, means forapplying'across one diagonal of the bridge structurean alternating current voltage of predetermined frequency,- and a seriescombination of a resistor and a variable direct current signalingvoltage source forming the opposite diagonal, whereby the potential dropacross the last named resistor due to the flowof current through therectifier occurs for time periods variable in accordance with thestrength of the direct current supplied from the direct current sourceserially connected therewith serving to modify the output energy fromthe rectifier.

3. The method of controlling the brilliance of electro-optical imagesproduced upon the fluorescent end wall of a cathode ray tube which com-.prises generating a cathode ray, projecting the generated ray towardthe fluorescent end wall of the tube, and deflecting the projected rayby rectified current potentials of zero value for a portion of the timeof control proportional to the intensity of fluorescence to berepresented to vary the intensity of the projected cathode ray streamreaching the said screen.

4. The method of controlling the brilliance of electro-optical imagesproduced upon the fluorescent end wall of a cathode ray tube whichcomprises generating a cathode ray, projecting the generated ray towardthe fluorescent end wall of the tube, and deflecting the projected rayby unidirectional potentials of a variable period of zero value controlto vary the intensity of the projected cathode ray stream reaching thesaid screen.

5. The method of controlling the brilliance of electro-optical imagesproduced upon the fluorescent end wall of a cathode ray tube whichcomprises generating a cathode ray, projecting the generated ray towardthe fluorescent end wall of the tube, and deflecting the projected rayby unidirectional potentials of other than sinusoidal wave formation andhaving a zero value for variable time periods to vary the intensity ofthe projected cathode ray stream reaching the said screen.

6. In a television receiver device a cathode ray image reconstructingtube provided with a fluorescent screen, means for developing a cathoderay to produce the fluorescent efiects upon the screen and means tocause the fluorescent eflects to traverse the screen according topredetermined pattern, an apertured electrode within the tube throughwhich the electrons are adapted to pass to the fluorescent screen, meansfor producing within the tube an electron beam deflecting electrostaticfield changing in intensity from zero intensity toward a maximum toregulate the time period during which the cathode ray pencil passesthrough the aperture in accordance with the zero value of the deflectingelectrostatic field, and rectifier means responsive to received signalsto vary the zero period of the field to produce in accordance with thetime period during which the deflecting field is of zero value varyingdegree of brilliance of the fluorescent efiects due to the impact of thecathode ray upon the screen.

7. In a cathode ray television system, a cathode-ray tube ccmprisingasource of cathode rays,

a fluorescent screen, an anode from which the generated electrons areprojected toward the screen, an apertured electrode in the path of theprojected electrons, a pair of deflecting plates intermediate the anodeand the apertured electrode, rectifier means for supplying to thedefleeting plates unilateral pulsating voltages of variable zeroamplitude duration for varying in accordance with the field intensityproduced thereby upon the deflecting electrodes the proportionate timeperiod of each cycle of the alternating current during; which thecathode ray pencil passes through the aperture of the aperturedelectrode toward the fluorescent screen to vary thereby in accordancewith the time of impact percycle of the deflecting-voltage thebrilliance of the resulting fluorescent efiect, and a plurality ofangularly disposed ray deflecting fields for causing the point of impactof the controlled cathode ray pencil to traverse according to apredetermined pattern substantially the entire area of the flucrescentscreeen.

8. A system for producing control voltages for use in connection with acathode ray tube having deflecting electrodes for controlling thecathode ray developed within the tube, which comprises a local source ofalternating current energy of substantially constant frequency, arectifying device connected with said source adapted normally to pass toits output circuit alternate half cycles of the generated alternatingcurrent, means controlled in accordance with received Signaling energyfor applying to the rectifying device direct current voltages so as tovary in accordance with the amplitude thereof the time period per cycleof the alternating current energy during which the rectifier outputremains at zero and electrical connections to supply the rectifieroutput energy to the deflecting electrodes to control the electron beamin accordance with said output energy.

9. The method of controlling the brilliance of electro-optical imagesproduced upon the fluorescent end wall of a cathode ray tube whichcomprises generating a cathode ray, projecting the generated ray towardthe fluorescent end wall of the tube, and deflecting the projected rayby undulating current potentials of zero value for a portion of the timeof control proportional to the intensity of fluorescence to berepresented to vary the intensity of the projected cathode ray streamreaching the said screen.

10. The method of controlling the brilliance of electro-optical imagesproduced upon the fluorescent end wall of a cathode ray tube whichcomprises generating a cathode ray, projecting the generated ray towardthe fluorescent end wall of the tube, and deflecting the projected rayby undulating current potentials of a variable zero value period ofcontrol to vary the intensity of the projected cathode ray streamreaching the said screen.

11. In a television receiver device a cathode ray image reconstructingtube provided with a fluorescent screen, means for developing a cathoderay to produce the fluorescent effects upon the screen and means tocause the fluorescent eflfects to traverse the screen according topredetermined pattern, an apertured electrode within the tube throughwhich the electrons are adapted to pass to the fluorescent screen, meansfor producing within the tube an electron beam deflecting electrostaticfield changing in intensity from zero intensity toward a maximum toregulate the time period during which the cathode ray pencil passesthrough the aperture in accordance with the zero value of the deflectingelectrostatic field, and means responsive to received signals to varythe zero period of the field to produce in accordance withthetime periodduring which the deflecting field is of zero value varying degrees ofbrilliance of the fluorescent effects due to the impact of the cathoderayupon the screen.

- l 12. In a cathode ray television system, a cathode ray tubecomprising a source of cathode rays,

a fluorescent screen, an anode from which the generated electrons areprojected toward the screen, an apertured electrode in the path of theprojected electrons, a pair of deflecting plates intermediate the anodeand the apertured electrode, means for supplying to the deflectingplates voltagesof variable-amplitude and of varying time period of zeromagnitude duration for vary- -ing in accordancewith the field intensityproto a predetermined pattern substantially the entire area of thefluorescent screen. DIETRICH PRINZ.

